Lopker, J. (2000). Pictures of personality: Guide to the four human natures (First edition.). Typology.
Chicago-viite (17. p.)Lopker, John. Pictures of Personality: Guide to the Four Human Natures. First edition. Los Angeles, CA: Typology, 2000.
MLA-viite (8. p.)Lopker, John. Pictures of Personality: Guide to the Four Human Natures. First edition. Typology, 2000.
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